1. Field of the Invention
The present invention relates to a disc cartridge to hold therein an optical disc (such as MO and DVD-ROM) or a similar disc-like recording medium.
2. Description of the Prior Art
For a greatly increased recording density through enhanced dust prevention, attempts have been made to develop a new disc cartridge with an inner rotor, as disclosed in the following patent literature.    Japanese Patent Laid-open No. 283556/2001 and its corresponding U.S. application, Ser. No. 09/82183    Japanese Patent Laid-open No. 332054/2001, its corresponding U.S. application, Ser. No. 09/858759, and its corresponding EP application, EP Publication No. 1156488
The disclosed disc cartridge has an inner rotor which is rotatably arranged between its upper and lower shells. On the bottom of the inner rotor is rotatably mounted an optical disc (such as MO and DVD), with its recording surface facing downward. The lower shell has a bottom opening (an elongated hole) to receive therein the optical pickup and the disk table of the spindle motor. In the bottom of the inner rotor is formed an internal opening of almost the same size and shape of the bottom opening. Between the lower shell and the bottom of the inner rotor are arranged two shutter members which, as the inner rotor rotates, open and close the opening in the bottom of the lower shell by their reciprocating movement between a first position at which the internal opening of the inner rotor coincides with the opening in the bottom of the lower shell and a second position which is displaced sideward from said first position.
Incidentally, at the center of the bottom of the inner rotor, there is a disc mount (semicircle or paired crescents in shape) which is formed integrally convex on the top of the periphery of the internal opening. On the disc mount is placed horizontally the center of an optical disc so that the recording surface (or the underside of the optical disc) floats above the bottom of the inner rotor while avoiding contact therewith. The inner rotor is driven by the following mechanism. The inner rotor has an integrally formed partial gear (to be driven) on its outer periphery. This gear is partly exposed in a window formed in one side of the disc cartridge. When the disc cartridge is loaded into a disc drive unit, the gear of the inner rotor engages with a driving rack of the disc drive unit. Thus the inner rotor is driven between the close position and the open position.
This disc cartridge is thin and holds therein an inner rotor and two shutter members (which are molded from plastics). Therefore, the two shutter members and the inner rotor are easily deformed inward when they are pressed inadvertently by the user's fingers while the opening at the bottom of the lower shell is closed by them. As the result of deformation, the two shutter members and the inner rotor come into contact with the recording surface (facing downward), thereby easily damaging data.
If a disc cartridge is to be made thin, it is necessary to reduce the height of the disc mount (shaped like a semicircle or paired crescents) on the inner rotor. This measure, however, results in the recording surface of the optical disc coming extremely close to the bottom of the inner rotor.
The above-mentioned disc mount shaped like a semicircle or paired crescents is so constructed as to permit the central part of an optical disc to be placed horizontally thereon. This disc mount, unlike the completely round disc mount on which the central part of an optical disc is placed horizontally, does not hold the central part of an optical disc by its entire periphery. Thus, the optical disc placed on the disc mount tends to incline toward an open part of the disc mount. The inclined disc causes its recording surface to come into contact with the bottom of the inner rotor, resulting in damage to data stored therein.
Meanwhile, the disc cartridge of two-head type for high-density recording, as disclosed in Japanese Patent Laid-open No. 332054/2001, is constructed such that the internal opening of the inner rotor is displaced sideward with respect to the opening in the bottom of the lower shell, and, when the disc cartridge is in its closed state (with the opening in the bottom of the lower shell closed by the two shutter members), the opening in the bottom of the inner rotor comes close to the window through which the inner rotor is driven, said window allowing the driven part opened in one side of the disc cartridge to be exposed. The above-mentioned disc cartridge in its closed state permits dust (together with the atmosphere) to get into the gap under the bottom of the inner rotor through the driving window of the inner rotor, with dust blowing up to the bottom of the inner rotor through the internal opening close to the driving window of the inner rotor, thereby sticking to the downwardly facing recording surface of the optical disc placed on the bottom of the inner rotor. Dust sticking to the recording surface of the optical disc causes spacing losses at the time of recording and reproduction. This is a serious drawback to high-density recording.